Proopiomelanocortin synthesis in the testes Spermatogenesis, the process by which the male germ cells are produced, is of prime importance to both human male fertility and reproductive processes in animals. Proopiomelanocortin (POMC) is known to be synthesized in the testes and is a precursor to several very important and biologically active peptides which include adreno corticotropin (ACTH), melanocyte- stimulating hormone (MSH), and beta-endorphin. POMC derived peptides are important in local regulation of the testes and may have two potential roles. First, these peptides may help maintain the structure and organization of the gonads for spermatozoa production. Second, POMC derived peptides from POMC may act peripherally to regulate the processes which are important for reproduction. The goal of this research is to localize POMC expression study its regulation by hormones. POMC synthesis has been reported in Leydig cells and in spermatocytes, however, other gonadal cell types may produce this precursor protein. This study is designed to localize the cell type or types in testes which synthesize proopiomelanocortin, first by selective cell depletion using irradiation to deplete the germ cells and second using ethane dimethylsulfonate to destroy mature Leydig cells. These studies will be conducted in combination with androgen maintenance, since mature Leydig cell loss deletes the endogenous source of testosterone. Second, hormonal regulation of proopiomelanocortin production will be evaluated in vivo, using hypophysectomized rats. The hormones, luteinizing hormone, prolactin, and follicle-stimulating hormone which have known effects on Leydig cells, Sertoli cells and germinal epithelium of the male gonad will be investigated for their effects on cell types which produce POMC. Insitu hybridization will be used to confirm northern analysis of mRNA for positive cell localization and to potentially confirm hormonal effects on POMC synthesis in vivo models. Regulation of POMC synthesis in the gonad may be very important and may provide insights for overall control of spermatogenesis.